Lecture_no10_10 - Lecture 10 Microelectronic Devices MOSFET regimes of operation saturation regime channel length modulation small signal equivalent

Lecture_no10_10 - Lecture 10 Microelectronic Devices MOSFET...

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1 Lecture 10 Microelectronic Devices MOSFET – regimes of operation – saturation regime – channel length modulation – small signal equivalent circuit MOSFET scaling – Dennard’s rule: constant-field – Short channel effects – CMOS technology trends CMOS performance factors Key questions What are the main operation regimes of MOSFET? How does the MOSFET work in saturation ? Does the pinch-off point represent a block to current flow? What is a small signal MOSFET equivalent circuit? Why we need it? How should one scale down the MOSFET: what is constant-field scaling rule? How the scaling affects the device (technological) parameters? 2 What is the short channel effect ? What is CMOS? What are the CMOS performance factors ?
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2 MOSFET I-V characteristics 3 MOSFET: low drain voltage, V DS A.M. Ionescu, 2008 4 Also modeled as resistor:
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3 MOSFET current calculation 5 MOSFET: pinch-off at high V DS 6
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4 What happens when V DSsat = V GS V T ? • Charge control relation at drain end of channel: Saturation (1) • No inversion layer at end of channel Pinch-off • At pinchoff: – electron concentration small but not zero – electrons move fast because electric 7 field is very high – dominant electrostatic feature: acceptor charge – there is no barrier to electron flow (on the contrary!) Transfer charact. Output charact. Saturation (2) SAT LIN Drain current at pinchoff: lateral electric field V DSsat = V GS V T electron concentration 8 V GS V T I Dsat (V GS V T ) 2 • I Dsat 1/ L
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5 Cutoff : V GS <V T (V GD <V T ): no inversion layer anywhere underneath gate MOSFET: regions of operation Linear : V GS >V T , (with V DS >0): inversion layer everywhere underneath gate 9 Saturation : V GS >V T , V DS > V G -V T =V Dsat MOSFET: channel length modulation (1) What happens if V DS > V DSsat = V GS V T ?
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  • Spring '12
  • aaa
  • Channel length modulation, signal equivalent circuit, small signal equivalent, A.M. Ionescu

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